1. Field of the Invention
This invention relates in general to batteries, more particularly to batteries that employ an electrically conductive flowing aqueous electrolyte, and most particularly to batteries that employ an electrically conductive flowing aqueous electrolyte in a stackable cell configuration.
2. Description of the Related Art
A pile configured battery cartridge consists of a group of electrochemical cells, two or more, comprised of flat plate electrodes mechanically stacked one on top of the other. The cell consists of a positive electrode, a negative electrode, and a cell gap separating the two into which a conductive electrolyte flows as required to allow conductive ionic species to transfer between the positive and negative cell electrodes while electrons, in the form of electrical current, flows from the cell via the positive cathode electrode and returns to the cell via the negative anode electrode.
By stacking two or more cells on top of each other, the anode of one cell adjacent to the cathode of the adjoining cell, and providing an electrical interface between adjacent cells, an electrical series connection of multiple single cells is achieved. Activation of the cells and the cell stack is achieved by introducing the appropriate electrolyte into each cell and providing an electrical connection between the anode and cathode on the opposite ends of the cell stack.
The electrochemical discharge reaction (reduction of the cathode and oxidation of the anode) occurring in each cell of the battery stack will continue as long as there are sufficient levels of chemical reactants, the physical integrity of the individual cell components is maintained, and the critical operating parameters, such as electrode temperature, are maintained at required levels. In many pile battery applications, such as an aluminum-silver oxide primary battery, the magnitude of electrical current conducted through the electrodes and electrolyte combined with the thermodynamic energy associated with the electrochemical and corrosion reactions, defined in Eqs 1 and 2, respectively,2Al+3AgO+2NaOH2NaAlO2+3Ag+H2O E′=2.88 v  (1)2Al+2H2O+2OH−2AIO˜+3H2 85.3 kcal/gmole Al  (2)is such that the rate and magnitude of heat resulting from these effects raises the temperature of the cell electrodes and electrolyte. In order that the cell temperature does not exceed an allowable threshold, heat generated inside the cell by the reactions described in Eqs. 1 and 2 must be removed by some mechanism. The mechanism of choice is by forced or natural convection utilizing the electrolyte as the convective media. This is accomplished by flowing the relatively low temperature electrolyte at a prescribed rate into and through the cell, thus transferring the heat from the cell into the electrolyte and out of the cell, thus maintaining the cell at the desired temperature. In order to maintain a uniform temperature distribution across the surface of an individual cell electrode, a uniform Reynolds number, i.e., mass flow rate of electrolyte, must exist across the electrode. A non, uniform flow distribution through an individual cell results in non uniform heat transfer resulting in a temperature gradient across the cell electrodes. The magnitude of the temperature gradient is proportional to the imbalance of the flow distribution. The impact of the temperature gradient are realized in the form of non uniform electrochemical and corrosion reactions described in Eqs. 1 and 2 resulting in non uniform electrode consumption and reduced cell operating efficiency.
In conjunction with the requirement for uniform mass flow within the individual electrochemical cell, it is imperative to maintain a uniform mass flow distribution to each of the individual cells comprising the multiple cell stack. This is necessary to assure uniform temperature from cell to cell, thus avoiding a temperature gradient among the individual cells. This has the same effect as described for the individual cell, non uniform electrode consumption among cells, non uniform electrochemical conversion efficiency and non uniform generation of reaction products from cell to cell, all of these result in reduced overall cartridge operating efficiency.
There are generally two types of pile battery construction. The first employs a one-piece cast manifold assembly. This consists of a hydraulic header, with either a tapered cross sectional area in the axial direction or a constant cross sectional area in the axial direction, off of which are networks of parallel hydraulic branches, spaced either uniformly or non uniformly as required to achieve uniform flow distribution, in the axial direction, through these lateral branches. These lateral branches indirectly feed individual cells or groups of cells in a battery cartridge electrode stack. Feeding would mean to provide hydraulic fluid, in this case conductive electrolyte, into a hydraulic plenum or raceway to which each cell, or a group of cells, in the cell stack would be in contact, hydraulically and electrically.
The lateral branches and fluid exit ports of the one-piece cast manifold assembly, here to fore also referred to as the cast manifold, are not mechanically connected to the individual cells within the cell stack. All of the hydraulic exit ports exiting the manifold and feeding the cell stack are hydraulically and electrically in contact with all of the cells in the cell stack. This is a major problem which resulted in a hydraulic distribution problem closely coupled. to an electrical circuit problem, each with diametrically opposed approaches to optimization. The hydraulic problem could not be addressed without having to address the electrical circuit problem and visa versa. This would not be an issue of concern if it was not for the fact that each of these problems are technically very complicated and, independent of each other, require a great deal of experimental and analytical study. The need to address just one of these problems automatically doubles the required level of effort.
A related problem with the cast manifold is that a manifold had to be custom fabricated for each specific cartridge containing a different number of cells. Any variation to the cartridge as a result of varying the number of cells the cartridge was to include required the design, fabrication and experimental evaluation of a new cast manifold assembly. This process could literally take years depending on the magnitude of the variations between cartridge sizes. It became readily apparent that in order to stay competitive it was necessary to design a manifold configuration that could be independent of the number of cells in a given cartridge configuration.
The inability to introduce multiple fluids, each one chemically unique, into each cell of the cartridge while maintaining the hydraulic separation of the fluids was not possible with a cast manifold assembly. In certain pile battery electrochemistry's, it is necessary to operate with separated flows, to do otherwise would render the electrochemistry so inefficient it could not be used. A method to accomplish this was needed.
As a result of the above referenced problems with a cast manifold assembly pile battery configuration, a one-piece injection molded manifold was developed. This manifold comprises a single manifold assembly for each cell, which contains all the hydraulic distribution network channels impressed into the assembly. This allowed for improved performance and cost reduction, but did not allow for separated flow via a single manifold nor did it allow for hydraulic sealing of adjacent manifolds independent of the compressive force applied to the manifold assembly. This manifold also did not decouple the hydraulic performance from the electrical performance of the manifold.
In order to address some of the limitations noted above, the invention disclosed in U.S. Pat. No. 4,735,630 was developed. The patent discloses a manifold assembly using a single manifold assembly for each cell of a pile configured battery that employs a series obstacles of “bumps” in the flow path of the electrolyte in order to ensure a uniform flow of electrolyte through the cells of the battery. While this configuration helped to avoid the problematic results of non-uniform flow of electrolyte through battery cells discussed above, it did not address the compressive force issue discussed above or allowed the introduction of more than one independent fluid pathway into a cell.
Therefore, it is desired to provide a method and device for sealing manifolds independent of the applied compressive force necessary to reduce tolerancing of the manifold assembly, thus reducing unit cost. It is also desired to provide a manifold assembly that allows operation of a cell within pile configured batteries using independent flows of electrolyte.